Yeah.. well that happens..
Simply reset the TC. No reset will delete stuff from the hard disk.
The airport utility is great when it all works but unfortunately is less than straightforward otherwise. Personally I use 5.6 utility even on Mountain Lion because it is easier IMHO to set things the way I want them .. than the way Apple automates it, over which you have no control.
You can load 5.6 utility into ML using the following trick. (see below).
Set all wireless names to SMB standard.. short, no spaces and pure alphanumeric.
Lock the wireless channels if you continue to have problems.
Or do the full reset. And simply start over the TC setup.
How to load 5.6 into ML.
1. Download 5.6 for Lion.
http://support.apple.com/kb/DL1482
Click to open the dmg but do not attempt to install the pkg.. it won't work anyway.
2. Download and install unpkg.
http://www.timdoug.com/unpkg/
Run unpkg on the desktop.. it is very simple.. drag the AirPortUtility56.pkg file over to unpkg.. and it will create a new directory of the same name on the desktop.. drill down.. applications utilities .. there lo and behold is Airport utility 5.6 .. drag it to your main utilities directory or just run it from current location.
You cannot uninstall 6.1 (now 6.2 if you updated) so don't try.. and you cannot or should not run them both at the same time.. so just ignore the toyland version.. the plastic hammer.. and start using 5.6.. a real tool.
For screen shots see this post.
https://discussions.apple.com/thread/4668746?tstart=0